This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. MD simulations provide new insights into protein-protein interactions;protein binding/dissociation events and the coupling of structural and dynamical changes across interfaces that is seen in cell signaling proteins. Plexin-B1 is a transmembrane receptor critical for neuronal and cardiovascular development, but also in cancer spreading (metastasis). An intracellular domain interacts directly with the small GTPases Rac1 and Rnd1. We are in the middle of an extensive experimental and computational project to understand this interaction and seek time on Aton to push our simulations into the multi-microsecond timescale to study the structure and dynamics of the plexin-B1/GTPase complexes.